The study of visual development has far surpassed that of auditory development, perhaps due to the lack of inexpensive, efficient, and simple methodology to investigate auditory behavior in nonverbal subjects. The Fantz visual selectivity paradigm has proven to be an effective method for the study of infant vision, allowing inferences about visual acuity, stimulus hierarchies, and maturational changes. In the past year at this laboratory, a simple operant procedure has been developed which is an auditory analogue to the Fantz visual selectivity paradigm. In this procedure, sounds are presented to infants contingent upon visual fixation to one of two identical, but separate displays. Differential response was found to the displays on the basis of the properties of the sounds with which they were associated, thus allowing assessment of infant auditory selectivity. Three different experiments are proposed to assess the utility of this paradigm. The first experiment will explore the feasibility of this method for testing auditory thresholds at various frequencies. The second experiment will test for an hypothesized preference for sounds with certain bandwidth characteristics. The third experiment will manipulate fundamental frequency and intonation of speech to determine those parameters which account for the previously demonstrated preference for speech.